Electronic postal/shipping scales (hereinafter "postal scales") are known. Prior art postal scales are described in U.S. Pat No. 4,718,506, and copending patent application Ser. No. 139,881, both of which are assigned to the assignee of this application and the disclosures of which are incorporated herein by reference.
The avoirdupois system of measuring weight, based on ounces and pounds, is used in the United States. The metric system of measuring weight, based on grams and kilograms, is used in Europe. In some countries both weight measuring systems are used.
The amount charged by parcel carriers (which term should be understood to include postal authorities) for carriage of a particular item often depends on the weight of the item, the desired destination for the item and the class of service to be provided. From this point forward "class" should be understood to mean a particular class of service provided by a particular parcel carrier. Typically for each class a rate table is provided which specifies the amount to be charged according to the weight category into which the item falls and, perhaps, also according to the zone in which the destination is located. The weight categories for a given rate table must, of course, be defined in terms of either avoirdupois or metric units. Some carriers, in some countries, may provide for a given class two rate tables, one defined in avoirdupois units and the other in metric units. For other classes, only one rate table is provided, the table being defined in one of the weight measuring systems.
Postal scales according to prior art have been able to display an item's weight either in avoirdupois or metric units, at the operator's option. But such prior art scales were capable of automatically calculating parcel rates only from rate tables defined in one of the weight measuring systems ("supported units") and not from rate tables defined in the other system ("nonsupported units"). Thus, if a user of such a scale desired to use a class for which the rate table was defined in the nonsupported units, he either had to manually calculate the rate from a printed rate chart or he had to employ a second postal scale that could calculate rates from a rate table defined in the nonsupported units.
Similar inconvenience arose for classes for which there were alternative rate tables, one defined in metric and the other in avoirdupois. For such classes the user might find it advantageous to compare the rates applicable to a particular item according to both tables in order to see if a rate according to one table was lower. For example, assume that for a particular class with alternative rate tables, the charge for shipping an item weighing one pound or less is $2.00, while the charge for an item weighing more than a pound but not more than two pounds is $2.50. Further assume that according to the metric rate table, the $2.00 charge applies to items weighing 500 grams or less, and the $2.50 charge applies to items weighing more than 500 grams but not more than a kilogram. For an item weighing more than a pound (454 grams) but not more than 500 grams, it would be advantageous to use the metric rate table, which provides a shipping charge of $2.00 as compared to the avoirdupois rate table, which provides a $2.50 charge. In such a case, with prior art scales, the user had to consult a second scale or a printed rate table, in order to compare the charges resulting from the alternative rate tables.